electrical engineering Mcqs
1. economics of power generation2. analog electronics3. solid state switching circuits4. parallel circuits5. switchgear and protection6. op amp circuits7. transistor audio power amplifiers8. electrostatics9. heating and welding10. multi stage transistor amplifiers11. passive filters12. network theorems13. regulated d c power supply14. a c fundamentals circuits and circuit theory15. electromagnetic induction16. power electronics17. magnetism and electromagnetism18. transformers19. modulation and demodulation20. d c generators21. semiconductor theory22. single phase induction motors23. semiconductor diode24. hybrid parameters25. digital electronics26. oscillators27. earthing or grounding28. single stage transistor amplifiers29. d c motors30. transistor biasing31. amplifiers with negative feedback32. basic electrical33. electronic instruments34. synchronous motors35. field effect transistors fet36. magnetic circuit37. control systems38. industrial drives39. power generation40. series parallel circuits41. transistor tuned amplifiers42. electrical engineering materials43. rectifiers and converters44. integrated circuits45. scr silicon controlled rectifiers46. cables47. polyphase induction motors48. measurement and instrumentation49. transistors50. electrical machine design51. electrolysis and storage of batteries52. electric traction53. transmission and distribution
4701. In a 3 phase VSI out of eight valid states, the number of valid states that produce zero ac line voltages is/are_________?
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A. two

B. One

C. Four

D. Three

4702. IGBT combines the advantages of_____________?
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A. SITs and MOSFETs

B. BJTs and SITs

C. BJTs and MOSFETs

D. None of these

4703. If energy is taken from the AC side of the inverter and sends it back into the DC side, then it is known as___________?
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A. None of these

B. Motoring mode operation

C. Braking mode operation

D. Regenerative mode operation
4704. Power electronics essentially deals with control of a.c. power at____________?
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A. 50 Hz frequency

B. Frequencies above 1000 kHz

C. Frequencies less than 10 Hz

D. Frequencies above 20 kHz

4705. A step up chopper has input voltage 110 V and output voltage 150 V. The value of duty cycle is_____?
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A. 0.27

B. 0.45

C. 0.32

D. 0.67

4706. If the gate voltage of an SCR is removed, then the_______________?
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A. cathode current increases

B. anode current increases

C. anode current does not decrease at all

D. anode current decreases

4707. A GTO can be turned on by applying___________?
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A. Positive gate signal

B. Positive drain signal

C. None of these

D. Positive source signal

4708. With gate open, the maximum anode current at which SCR is turned off from ON condition is called____________?
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A. peak reverse voltage

B. breakdown voltage

C. latching current

D. holding current
4709. The conduction losses in IGBT is____________?
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A. Equal to that of MOSFET

B. More than that of MOSFET

C. Lower than that of MOSFET

D. Equal to that of BJT

4710. Which of the following is true about SIT?
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A. SIT is a high power, high frequency device

B. SIT is a low power, high frequency device

C. SIT is a high power, high voltage device

D. SIT is a high power, low frequency device

4711. Example of a voltage clamping device______________?
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A. snubber circuit

B. fast acting fuse

C. aluminium block

D. metal oxide varistor
4712. What is used to protect the SCR from over current ________________?
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A. Heat sink.

B. CB and fuse.

C. Snubber circuit.

D. Voltage clamping device.

4713. SITH is also known as___________?
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A. None of these

B. Filled controlled diode

C. Filled controlled rectifier

D. Silicon controlled rectifier

4714. A silicon controlled racitifier (SCR) is a ____________?
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A. Device with three junction

B. Unijunction device

C. Device with four junction

D. None of the above

4715. TRIAC is a semiconductor power electronic device which contains____________?
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A. Two SCRs connected in parallel

B. Two BJTs connected in series

C. Two SCRs connected in series

D. Two SCRs connected in reverse parallel
4716. In dual converters________________?
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A. Both rectifiers provides positive current to the load

B. Both rectifiers provide negative current to the load

C. One rectifiers provide positive current to the load and the other negative current

D. One rectifier provide positive current to the source and the other negative current to the load

4717. A Triac is a ______________?
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A. 3 terminal bidirectional switch

B. 3 terminal bilateral switch

C. 2 terminal bilateral switch

D. 2 terminal switch

4718. Delay time is defined by the interval when_______________?
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A. anode voltage drops from 100 % to 90 % of its actual value

B. all of these

C. gate current increases from 90 % to 100 % of its final value

D. anode current reaches 10 % from forward leakage current

4719. An RC snubber network used in BJT__________?
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A. Divert the collector current during turn off

B. Dissipates a fair amount of switching power

C. All of these

D. Improves the reverse bias safe operating area

4720. For an SCR gate aEUR" cathode characteristic is a straight line of 130. For triggered source volume of 15 V and allowable gate power dissipation of 0.5 W compute the gate source resistance_____?
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A. 108 I.

B. 111.9 I.

C. 11.19 I.

D. 115 I

4721. 4 thyristors rated 200 V in series. The operating voltage of the string is 600 V. Derating factor of the string is_____________________?
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A. 0.2

B. 0.25

C. 0.7

D. 0.75

4722. Rise time is defined by the interval when____________?
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A. gate current rises from 90 % to 100 % of it final value

B. anode voltage drops from 90 % to 10 % of its initial value

C. anode current rises 10 % to 90 % of its final value

D. both B and C
4723. CB used for over current protection of thyristor operates when the fault current is__________?
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A. of long period

B. of short duration

C. both (A) and (B)

D. neither (A) nor (B)

4724. In forward blocking mode of a thyristor________?
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A. Junction J1, J3 is in reverse bias and J2 is in forward bias.

B. junction J3 is in forward bias and J1, J2 is in reverse bias.

C. junction J2 is in reverse bias and J1, J3 is in forward bias.

D. Junction J1 and J2 is in forward bias and J3 is in reverse bias.

4725. In a 3 phase CSI, if the required line output voltages are balanced and 120 degree out of phase, then the chopping angles are used to eliminate only the harmonics at frequencies
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A. All of these

B. 11

C. 5

D. 7

4726. Harmonics in 3 phase inverters can be reduced by using___________?
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A. Passive filter

B. Active filter

C. Both passive and active filters

D. None of these

4727. In a flyback converter, the inductor of the buck-boost converter has been replaced by a_____________?
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A. Flyback transistor

B. Flyback capacitor

C. Flyback resistor

D. Flyback transformer
4728. During gate recovery time_____________?
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A. charge carriers of J3 junction is removed

B. charge carrier of J1 junction removed

C. charge carriers of J2 junction is swept out

D. charge carriers of J2 junction recombined
4729. The sum of all phase current in a star connected primary winding with no neutral connection is equal to___________?
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A. Three times the line current

B. Zero at all times

C. Three times the phase current

D. Phase current

4730. Maximum power loss occurs during_________________?
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A. rise time

B. all

C. delay time

D. spread time

4731. In ac dc conversion, when the switch is closed then the sum of voltages around the loop is____________?
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A. Non zero

B. Zero

C. Twice of the voltage when switch is open

D. Equal to the sum of voltage when switch is open

4732. Thermal voltage VT can be given by____________?
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A. (K2/q)(T + 1/T 1)

B. qT/K

C. KT/q

D. Kq/T

4733. A power semiconductor may undergo damage due to____________?
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A. Low di/dt

B. High dv/dt

C. Low dv/dt

D. High di/dt
4734. A single phase one pulse controlled circuit has a resistance R and counter emf E load 400 sin(314 t) as the source voltage. For a load counter emf of 200 V, the range of firing angle control is _____?
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A. 30 to 180.

B. 60 to 180.

C. 30 to 150.

D. 60 to 120.

4735. If the firing angle becomes negative, then the rectifier begins to work as_______________?
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A. A regulator

B. An inverter

C. A rectifier

D. A chopper

4736. For similar carrier and modulating signals, the line current used in CSI is_____________?
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A. Identical to phase voltage in CSI

B. Identical to phase voltage in VSI

C. Identical to line voltage in a VSI

D. Identical to line current in VSI

4737. Transformer utilization factor is a measure of the merit of a rectifier circuit. It is the ratio of_______________?
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A. AC input power to the transformer volt amp rating required by secondary

B. DC output power to the transformer volt amp rating required by primary

C. DC output power to the transformer volt amp rating required by secondary

D. AC input power to the transformer volt amp rating required by primary

4738. The advantage of using free wheeling diode in half controlled bridge converter is that
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A. There is always a path for the ac current independent of the ac line

B. There is always a path for the dc current independent of the ac line

C. There is always a path for the dc current dependent of the ac line

D. There is always a path for the ac current independent of the ac line

4739. In the operation and control of both naturally commutated and forced commutated SCR base converter, commutation plays an important role. The converters is / are ___________?
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A. All of these

B. DC AC

C. AC DC

D. DC DC

4740. What is the advantage of HRC fuses over Rewirable fuses?
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A. All of the above

B. High rupturing capacity

C. High speed operation

D. No ageing effect

4741. An SCR is made up of silicon because?
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A. silicon has small leakage voltage than germanium

B. silicon has small leakage current than germanium

C. silicon has large leakage voltage than germanium

D. silicon has large leakage current than germanium

4742. The turn-on time of an SCR with inductive load is 20 s. The puls train frequency is 2.5 KHz with a mark/space ratio of 1/10, then SCR will___________?
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A. Turn on if pulse frequency us increased to two times

B. Not turn on

C. Turn on

D. Turn on if inductance is removed

4743. Which one is most suitable power device for high frequency (>100 KHz) switching application?
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A. BJT

B. Schottky diode

C. Microwave transistor

D. Power MOSFET
4744. In variable frequency, PWM gain
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A. Phase lead helps to increase the phase margin of the control loop

B. Phase lag helps to decrease the phase margin of the control loop

C. Phase lag helps to increase the phase margin of the control loop

D. Phase lead helps to decrease the phase margin of the control loop

4745. A thyristor is basically________?
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A. A set of SCRs

B. PNPN device

C. A set if SCR,diac and triac

D. A combination of diac and triac

4746. A carrier based PWM technique in CSI is composed of____________?
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A. A switching and shorting pulse combination

B. All of these

C. A switching pulse generator and a shorting pulse generator

D. A shorting pulse distributor

4747. Under harmonic free load voltages, the 3 phase VSI_____________?
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A. Does not contains fifth harmonic

B. Does not contains seventh harmonic

C. Does not contains second harmonic

D. Does not contains third harmonic

4748. Dynamic equalising circuit is useful____________?
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A. To limit di / dt of SCR

B. To limit dV / dt of SCR

C. For voltage equalisation

D. Both B and C
4749. A single phase ac dc converter is also known as____________?
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A. rectifier

B. regulator

C. chopper

D. inverter

4750. A MOSFET, for its conduction uses_____________?
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A. Only minority carriers

B. Only majority carriers

C. Both minority and majority carriers

D. None of these